Patent Application
20160186537
For over a century in the oil and gas industry, most downhole fluid is pumped using conventional pump jack systems. These conventional systems require large transportation costs due to their tremendous weights and sizes. Conventional pump jack systems also encounter difficulties in controlling operating parameters, difficulties in system adjustments, and high installation costs. Adjustments to the conventional pumping units involve separately adjusting stroke length, upstroke speed, and downstroke speed, which requires manpower and a lift crane to pin and unpin the shaft and to adjust counterweight positions. These adjustments are costly and involve safety risks.
Most hydraulic pump jack drive systems directly lift both the rod string and fluid head inside the tubing string, which consumes a large amount of power. These systems are typically used for low production margin wells. Certain hydraulic pump jack systems save energy via N2 counterweight systems, but stroke length and seal life are reduced in these systems for high speed operations.
Desirable improvements to pump jack systems include decreased weight and size, ease of controlling the system remotely, and increased power, system efficiency, and reliability of the drive.
A pump jack system may be used for reciprocating a down hole pump via a sucker rod string in an oil and gas well. The pump jack system may include a cylinder assembly for providing upward and downward movement of the sucker rod string. The cylinder assembly may be mounted directly above a wellhead of the oil and gas well. Alternatively, the cylinder assembly may be mounted near the wellhead. In this embodiment, the pump jack system may further include a sheave assembly connected to the cylinder assembly, with the sheave assembly having a carrier assembly disposed above the wellhead.
In one embodiment, drive piston 20 may be integrally formed with a lower end of drive rod 22. Similarly, balance pistons 30 and 42 may be integrally formed with lower ends balance rods 32 and 44, respectively. Alternatively, drive piston 20 and balance pistons 30, 42 may each be securely affixed to lower ends of drive rod 22 and balance rods 32, 44, respectively, such as by bolted connection or any other connection mechanism capable of securely fastening drive piston 20 to drive rod 22.
Upper ends of drive barrel 18 and balance barrels 28 and 40 may be fixed to upper cross member 52, and lower ends of drive barrel 18 and balance barrels 28 and 40 may be fixed to lower cross member 54. Upper and lower cross members 52 and 54 secure barrels 18, 28, and 40 in a fixed arrangement. In one embodiment, drive barrel 18 is disposed between balance barrels 28 and 40. Upper ends of drive rod 22 and balance rods 32 and 44 may be connected to rod cross member 56, such as with nuts 58. Rod cross member 56 rigidly connects drive rod 22 to balance rods 32 and 44 such that pistons 20, 30, 42 move in tandem within barrels 18, 28, 40, respectively. Seal members 60 are disposed within the annular space between rods 22, 32, 44 and the upper ends of barrels 18, 28, 40, respectively. Seal members 60 provide a fluid seal for drive chamber 26 and upper balance chambers 36 and 48.
In one embodiment, a net lifting area of drive chamber 26 may be equal to or nearly equal to a net lowering area of upper balance chambers 36 and 48 of balance cylinders 14 and 16. In other words, the area of lower surface 62 of drive piston 20 is approximately equal to the sum of the areas of upper surface 64 of balance piston 30 and upper surface 66 of balance piston 42.
Pumping fluid from fluid reservoir 102 into drive chamber 26 may push drive piston 20 upward. Upward movement of drive piston 20 lifts rod cross member 56 and balance pistons 30 and 42 by the same distance. As balance pistons 30 and 42 are lifted, fluid may be transferred from bladder accumulator into lower balance chambers 38 and 50 due to the pressure differential caused by balance pistons 30 and 42 being lifted. Fluid may also be displaced from upper balance chambers 36 and 48 through upper balance ports (described below) with upward movement of balance pistons 30 and 42.
Discontinuing the pumping of fluid into drive chamber 26 and pumping fluid from fluid reservoir 102 into upper balance chambers 36 and 48 may push balance pistons 30 and 42 downward. Downward movement of balance pistons 30 and 42 transfers fluid from lower balance chambers 38 and 50 back into bladder accumulator 100. Forced downward movement of balance pistons 30 and 42 pulls drive piston 20 downward by the same distance due to rod cross member 56. Fluid passages 24 facilitate the downward movement of drive piston 20. With the downward movement of drive piston 20, fluid may be displaced from drive chamber 26 through a drive port (described below). Because of the fluid connections between upper balance chambers 36 and 48 and the fluid connections between lower balance chambers 38 and 50, cylinder assembly 10 may functionally have three chambers: first, drive chamber 26 for providing upward displacement of pistons 20, 30, 42; second, lower balance chambers 38, 50 for counterbalance purposes; and third, upper balance chambers 36, 48 for providing downward displacement of pistons 20, 30, 42. It should be noted that cylinder assembly 70, which includes drive rod 78 having axial bore 84, may be used with bladder accumulator 100.
With reference to
The fluid pumped from fluid reservoir 102 into drive chamber 26 or 82 and upper balance chambers 36, 48 may be a hydraulic fluid. The fluid pumped from bladder accumulator 100 into lower balance chambers 38, 50 may be a hydraulic fluid.
In this embodiment, upward movement of drive piston 20 may cause upward movement of balance pistons 30 and 42. This upward movement of balance pistons 30 and 42 may cause fluid to be transferred from lower accumulator chamber 132 into lower balance chambers 38 and 50 due to the pressure differential created by movement of balance pistons 30 and 42. Fluid transfer out of lower balance chambers 38 and 50 may cause downward movement of accumulator piston 126 and fluid movement from supply unit 134 into upper accumulator chamber 130 due to the pressure differential created by movement of accumulator piston 126. Downward movement of drive piston 20 and balance pistons 30 and 42 may cause fluid to be returned from lower balance chambers 38 and 50 into lower accumulator chamber 132, upward movement of accumulator piston 126, and fluid transfer from upper accumulator chamber 130 into supply unit 134.
The fluid moved between lower accumulator chamber 132 and lower balance chambers 38 and 50 may be a hydraulic fluid. In one embodiment, supply unit 134 contains one or more N2 gas bottles and upper accumulator chamber 132 may be configured to hold N2 gas. Alternatively, supply unit 134 may contain N2 gas or dry air.
Referring to
As pistons 20, 30, 42 and rod cross member 56 move upward (as described above), sheave 152 and rod clamp members 166 are moved upward. Similarly, as pistons 20, 30, 42 and rod cross member 56 move downward, sheave 152 and rod clamp members 166 are moved downward. A single wire line 160 or multiple wire lines 160 may be disposed around each sheave 152. It should be noted that sheave assembly 150 may also be used with cylinder assembly 10, cylinder assembly 70, or cylinder assembly 140.
With reference now to
Leak detection system 182 may include base member 184 having aperture 186 with upper radial shoulder 188. Leak detection system 182 may also include ram member 190 having radial extension 192. Ram member 190 and spring member 194 may be disposed within aperture 186 of base member 184. Spring member 194 may bias radial extension 192 of ram member 190 in an upward direction, such that in a neutral position, radial extension 192 engages upper radial shoulder 188 of base member 184. In the neutral position, upper end 196 of ram member 190 may extend beyond base member 184 into accumulator chamber 132, and lower end 198 of ram member 190 may be disposed within aperture 200 of lower cross member 54.
If fluid is leaking from lower accumulator chamber 132 and/or lower balance chambers 38, 50, accumulator piston 126 will continue to move downward until lower surface 202 of accumulator piston 126 engages upper end 196 of ram member 190 and moves ram member 190 downward by compressing spring member 194. As ram member 190 moves downward, lower end 198 of ram member 190 extends beyond lower surface 204 of lower cross member 54, which is detected by proximate sensor 206 held below lower cross member 54 with sensor holder 208. In response, proximate sensor 206 may cause a control system to reset ram member 190 to the neutral position. An increase in the frequency of lower end 198 of ram member 190 extending beyond lower surface 204 of lower cross member 54 indicates a fluid leak from lower accumulator chamber 132 and/or lower balance chambers 38, 50. In response to detection of a leak, seals of these chambers may be inspected or replaced.
With rod clamp members 166 in line with a center point of wellhead 212, rod clamp members 166 may be connected to sucker rod string 236. Sucker rod string 236 may extend through wellhead 212 and the associated oil and gas well to a downhole pump. Vertical reciprocation of sucker rod string 236 may power the downhole pump to allow for pumping fluid from the well to the surface. Pump jack system 210 may vertically reciprocate sucker rod string 236. Fluid may be fed into drive chamber 26 to raise drive piston 20, rod cross member 56, and sheaves 152. Fluid may be fed into lower balance chambers 38, 50 from an accumulator (e.g., a bladder accumulator or an accumulator cylinder) to provide counterbalance during the upstroke. Sheaves 152 may rotate as they are lifted such that the circumferential surface of sheaves 152 rotates along and takes up a length of wire line 160, which in turn lifts rod clamp members 166 and connected sucker rod string 236. Fluid may then be fed into upper balance chambers 36, 48 in order to lower balance pistons 30 and 42, rod cross member 56, and sheaves 150. Fluid may be returned from lower balance chambers 38, 50 to the accumulator. Sheaves 152 may rotate as they are lowered such that the circumferential surface of sheaves 152 rotates along and releases a length of wire line 160, which in turn lowers rod clamp members 166 and connected sucker rod string 236. This process is described in more detail above. In this way, pump jack system 210 may be used to vertically reciprocate a sucker rod string in order to power a downhole pump.
In one alternate embodiment, vertical support pipes 224 may be directly attached to a concrete block that is partially buried in the ground.
Sucker rod string 254 may extend below cylinder assembly 140, through wellhead flange 252, and into the oil and gas well below. A lower end of sucker rod string 254 may be in communication with a down hole pump. Vertical reciprocation of sucker rod string 254 may power the down hole pump for pumping fluid from the well to the surface. Pump jack system 250 may vertically reciprocate sucker rod string 254.
Fluid may be fed into drive chamber 82 to raise drive piston 76 and rod cross member 56, which in turn lifts sucker rod string 254 through sucker rod clamp 256. Fluid may be fed into lower balance chambers 38, 50 from an accumulator (e.g., a bladder accumulator or an accumulator cylinder) to provide counterbalance during the upstroke. Fluid may then be fed into upper balance chambers 36, 48 in order to lower balance pistons 30, 42 and rod cross member 56, which in turn lowers sucker rod string 254 through sucker rod clamp 256. Fluid may be returned from lower balance chambers 38, 50 to the accumulator. This process is described in more detail above. In this way, pump jack system 250 may be used to vertically reciprocate a sucker rod string in order to power a downhole pump.
While preferred embodiments of the present invention have been described, it is to be understood that the embodiments are illustrative only and that the scope of the invention is to be defined solely by the appended claims when accorded a full range of equivalents, many variations and modifications naturally occurring to those skilled in the art from a review hereof.
